I completely agree that some way of measuring the potential usefulness
of packages would be great.
To some extent, you can get a measure of the popularity of various
packages in Debian (and probably other Linux distributions have similar
systems). E.g.
http://qa.debian.org/popcon.php?package=ghc6
Not too many libraries yet, though.
-k
--
If I haven't seen further, it is by standing in the footprints of giants